Procedure and apparatus for improving a plasma accelerator plating apparatus used for diamond plating

ABSTRACT

A plating apparatus used in a diamond plating process in which a first electrode having a surface from which plating material is released is located in connection with a firing electrode to generate a first arc, the first arc being used to start a second arc between the first electrode and a second electrode, and in which apparatus a plasma spray formed from plating material released from the first electrode is directed toward a substrate to be plated includes a grinding element in contact with the surface of the first electrode and a mechanism for rotating the surface of the first electrode. The grinding element may be a firing electrode or an abrading tool. A method of operating the plating apparatus includes abrading the surface of the first electrode from which plating material is released.

FIELD OF THE INVENTION

The present invention relates to a plating apparatus used in a diamondplating process and a method of operating the plating apparatus.

BACKGROUND OF THE INVENTION

Diamond and diamondlike platings and films have a number of propertiesresembling those of corresponding traditional diamonds. The firstproperty is hardness. Another significant mechanical property is a lowfriction coefficient. The resistance to wear is also excellent.Moreover, such a plating or film remains unchanged in all known basesand acids. Thus, diamondlike platings and films are especiallyapplicable for the coating of bodies subject to wear and corrosion, suchas non-lubricated bearings. Another notable feature is the highrefraction coefficient of diamonds.

WO publication 89/06708 presents an apparatus for diamond plating. Theapparatus described in this publication works by forming from carbon bymeans of a plasma accelerator a plasma spray which is accelerated anddeflected toward the body to be plated. The plasma accelerator has acylindrical graphite cathode, A conducting rod serving as a firingdevice is placed inside the cathode.

During plating, carbon in the form of charged ions and uncharged atomsis released from the cathode. The surface of the cathode which releasescarbon is subject to erosion, which may manifest itself, e.g., in theform of microscopic holes appearing in the cathode surface, producingspongy structures. At first, the arc is normally started from thecathode surface, but with the progress of erosion the starting of thearc occurs more and more frequently at the bottom of the holes.Gradually the holes are covered up and the cathode becomes incapable ofemitting a plasma pulse.

For this reason, the cathode surface has to be smoothed out. This isgenerally accomplished by removing the cathode and refacing it, e.g., byturning. This is a complicated procedure, however. Moreover, it isimpossible to keep the plating apparatus running continuously for a longtime. Typically, the cathode has to be refaced every few hours.

SUMMARY OF THE INVENTION

The object of the present invention is to achieve an improvement indiamond plating equipment using known techniques. The procedure of theinvention for improving a plating apparatus is characterized in that theplasma surface of the cathode is continuously ground by means of agrinding blade or other equivalent grinding device.

Using the procedure of the invention, it is possible to achieve adecisive improvement in the usability of a diamond plating apparatus.The procedure of the invention allows continuous use of the platingapparatus as it does not require removal of the cathode for grinding orturning.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described in detail by the aid of anexample by referring to the attached drawings, in which:

FIG. 1 presents a diamond plating apparatus as described in WOpublication 89-06708; and

FIG. 2 presents a diamond plating apparatus according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Using a plasma accelerator, a plasma spray is produced from carbon andaccelerated toward the body to be plated. The plasma spray is deflectedby means of a magnetic field, whereupon it hits the surface of the bodyunder treatment. Both the plasma accelerator and the body being platedare placed in a vacuum.

Referring to FIG. 1, the plasma accelerator has a cylindrical cathode 1consisting of solid carbon. The cathode is connected to the negativeterminal of a first voltage source and to one terminal of a firstcapacitor C1. A discoidal anode 3 with a hole in the middle is connectedto a cylindrical coil 4 made of copper wire. The coil has a bent shapeand one end thereof is connected to the positive terminal of the firstvoltage source and to the other terminal of the first capacitor C1. Alsoconnected to the terminals of capacitor C1 are a diode D and anadjustable resistor R. The cathode 1 is partly surrounded by the coil 4and the anode 3 is completely surrounded by the coil 4.

Inside the cathode 1 is a conducting metal rod 5. Together with a secondvoltage source 6 and a second capacitor C2, the cathode 1 and the metalrod 5 form a firing circuit. The second voltage source 6 is adjustable.The cathode 1 is connected to the positive terminal of the secondvoltage source 6 and to one terminal of the second capacitor C2. Themetal rod 5 is connected to the negative terminal of the second voltagesource 6 and to the other terminal of the second capacitor C2.

A substrate 7 is plated by means of the plasma accelerator as follows.From the first voltage source 2, the first capacitor C1, connected inparallel with it, is charged. From the second voltage source 6, thesecond capacitor C2, which is connected in parallel with this voltagesource, is charged until a spark-over occurs in the air gap between thecathode 1 and the metal rod 5, producing an arc in this air gap. Thisarc discharges the second capacitor C2 and strikes another arc betweenthe cathode 1 and the anode 3. In this situation, the cathode 1 beginsto release carbon in the form of charged ions and uncharged atoms. Thearc between cathode 1 and anode 3 causes the first capacitor C1 to bedischarged. The arc is extinguished when the capacitor voltage fallsbelow the level required for sustaining an arc. In this way, the carbonions and atoms form a pulsed-shaped plasma spray. The pulse duration isdetermined by the capacitance of capacitor C1.

Connected in parallel with the first capacitor C1 are a diode D, whosefunction is to eliminate the opposing voltage produced at the terminalsof the first capacitor C1 by the oscillating circuit formed by the firstcapacitor Cl and the winding 4, and an adjustable resistor R protectingthe diode D.

The plasma spray is accelerated by the magnetic field generated by thewinding 4. Since the winding has a bent shape, the charged ions passingthrough the hole 8 in the anode 3 are deflected by the magnetic field,whereas the uncharged particles advance straight ahead withoutencountering the substrate 7 and are thus separated from the chargedions. The substrate 7 to be plated is placed near that end of thewinding 4 which is connected to the first voltage source 2 and firstcapacitor C1. Since the magnetic field generated by the winding deflectsthe charged ions but not the uncharged particles, the substrate to beplated is bombarded only by ions accelerated by the magnetic field.

FIG. 2 presents a diamond plating apparatus in accordance with thepresent invention. The apparatus has a solid barlike graphite cathode1'. The firing electrode 5' is placed near the end face (emittingsurface) 10' of the cathode, from which the carbon used for the platingis released. The firing electrode 5', whose lower surface is in contactwith the cathode, is a rectangular body of a width nearly equal to theradius of the cathode. Placed on the emitting surface 10' is an abradingtool 11' provided with a sharp abrading surface which has a widthslightly exceeding the radius of the cathode 1'. The abrading tool 11'is placed in contact with the end face (emitting surface) 10' of thecathode.

During plating, the cathode 1' is rotated about its longitudinal axis12' by means of a rotating mechanism (not shown). Thus, the end face(emitting surface) 10' of the cathode is continuously ground by theabrading tool and therefore remains smooth all the time. The cathodesurface is also abraded by the firing electrode. The rotating mechanismcan also be provided with, e.g., hydraulic equipment designed to pushthe cathode toward the abrading tool 11' according to the erosion of theemitting surface 10'. In this case the abrading tool 11' also serves asa motion limiter.

It is obvious to a person skilled in the art that different embodimentsof the invention are not restricted to the examples described above, butthat they may instead be varied within the scope of the followingclaims.

We claim:
 1. A method of operating a plating apparatus used in a diamondplating process, in which plating process a first arc is started betweena first electrode having a surface from which plating material isreleased, and a firing electrode placed in connection to the firstelectrode, another arc is started by means of the first arc between thefirst electrode and a second electrode, and a plasma beam formed fromplating material released from the surface of the first electrode isdirected toward the substrate to be plated,said method comprisingabrading the surface of the first electrode from which plating materialis released.
 2. The method of claim 1, wherein the surface of the firstelectrode is abraded by placing a grinding element in contact with thesurface and moving the surface relative to the grinding element.
 3. Themethod of claim 2, wherein the surface of the first electrode isrotated.
 4. The method of claim 1, wherein the surface of the firstelectrode is abraded by placing a grinding element in contact with thesurface and moving the grinding element relative to the surface.
 5. Incombination with a plating apparatus used in a diamond plating processin which a first electrode having a surface from which plating materialis released is located in connection with a firing electrode to generatea first arc, said first arc being used to start a second arc between thefirst electrode and a second electrode, and in which apparatus a plasmaspray formed from plating material released from the first electrode isdirected toward a substrate to be plated,means for abrading the surfaceof the first electrode from which plating material is released.
 6. Thecombination of claim 5, further comprising means for compensating forthe erosion of the first electrode, said compensating means beingadapted to move the first electrode according to the degree of erosionso that the surface thereof remains essentially in the same locationrelative to the means for abrading.
 7. In combination with a platingapparatus used in a diamond plating process in which a first electrodehaving a surface from which plating material is released is located inconnection with a firing electrode to generate a first arc, said firstarc being used to start a second arc between the first electrode and asecond electrode, and in which apparatus a plasma spray formed fromplating material released from the first electrode is directed toward asubstrate to be plated,a grinding element in contact with the surface ofthe first electrode; and means for rotating the surface of the firstelectrode.
 8. The combination of claim 7, wherein the grinding elementis a firing electrode.
 9. The combination of claim 7, wherein thegrinding element is an abrading tool.
 10. The combination of claim 7,further comprising means for compensating for the erosion of the firstelectrode, said compensating means being adapted to move the firstelectrode according to the degree of erosion so that the surface thereofremains essentially in the same location relative to the grindingelement.